1. Field of the Invention
This invention relates to a drive for a displaceable motor vehicle part, especially the cover element of an openable motor vehicle roof which comprises at least one drive cable and one driven output pinion.
2. Description of Related Art
Drives of the above mentioned type are widely used, for example, for covers of sliding roofs and the like, generally, the output pinion being driven by an electric motor via a stepdown gear and being made as a gear wheel which is located between two parallel drive cables made as ascending cables, and which drives the cables in opposite directions by direct engagement at one point of each cable at any given time, see for example, German Patent No. DE43 13687C2.
Furthermore, for example, German Patent No. DE 197 34 815 C1 discloses tandem drives for adjustable motor vehicle roof elements, in which there are two separate output pinions which are each driven by its own electric motor via its own step-down gear, and are directly engaged to two drive cables between them in order to drive them in opposite directions by engagement at one point of each cable at any given time. In this arrangement, the force is applied to each of the two drive cables at two successive points; however, for this purpose, there are two separate drives, and this represents high cost.
These known drives are disadvantageous in that, when high torque is applied to the output pinion, the point at which the force is applied to the respective drive cable is highly loaded, and this can lead to cable-side or pinion-side rupture.
The primary object of the present invention is to devise a drive for an displaceable motor vehicle part, such as a sunroof cover panel, which enables forces to be applied by the output pinion to the drive cable or cables which are higher possible with the prior art.
This object is achieved in accordance with the invention by a drive in which the output pinion is in driving engagement with a drive unit which, in turn, is in driving engagement with the at least one drive cable at least at two points. In this approach, it is advantageous that the drive force made available by the output pinion is applied to the drive cable or cables at least at two points so that the individual point of force application, as compared to known drives in which the force is applied to the drive cable at only one point at a time, is greatly reduced, generally at least cut in half.
Preferably, the drive unit comprises at least two wheels which each engage the drive cable or cables, and it is made as a gear reducer for rotation of the output pinion, it being possible for the wheels to be made as gear wheels and the drive cable or cables as threaded cables.
In the first embodiment, the drive unit comprises a total of two wheels which directly engage the output pinion, the output pinion engaging the teeth of the wheels and the output pinion and the wheels lying essentially in one plane. The diameter or the number of teeth of the two wheels can be slightly different, the diameter or the number of teeth of the output pinion for purposes of gear reduction preferably being less than for the wheels. In this embodiment the simple version is advantageous.
In one alternative embodiment, the drive unit is made such that the wheels which engage the cables are driven via gearing by the output pinion, the latter being made preferably such that the drive unit has two wheels which engage the cables and two wheels which are coaxial thereto and which are connected so as to rotate together, and which each directly engage the output pinion. In this embodiment, it is advantageous that the corresponding configuration of the individual wheels enable stronger gear reduction than in the first embodiment.
In the following, two embodiments of the invention are explained in detail, by way of example, using the attached drawings.